Imagemagick convert massively increasing filesize?

Question

I want to resize some PNG images with imagemagick, but it's making the files 5 times larger when I convert them:

$ convert -resize 50% -quality 80 01.png 01_half.png
$ ls -hal 01*.*
-rw-rw-r-- 1 3.3M Sep  9 09:05 01_half.png
-rwxr-xr-x 1 651K Jan 13  2011 01.png

From 651KB to 3.3MB! Can anyone suggest how to stop this happening?

Just noticed that this is a possible duplicate of the (unanswered) http://stackoverflow.com/questions/1492056/imagemagick-png-resize-increases-file-size — Richard, Sep 09 '11 at 14:12
Not really a programming question - try http://superuser.com ? — Paul R, Sep 09 '11 at 14:12

score 1 · Answer 1 · answered Sep 09 '11 at 14:18

1

Please note that ImageMagick's quality option's behavior is different with PNG's than it is with eg JPG's, and 80 looks like a pretty odd value for PNG's. As explained in the manual quality's value is cut in 2 where the first digit controls the zlib compression factor, and the second digit controls the filter type.

answered Sep 09 '11 at 14:18

fvu

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Just tried without the `-quality` option, and it resizes it to 3.7MB. – Richard Sep 09 '11 at 14:26
@richard weird... check http://www.imagemagick.org/Usage/formats/#png_quality for extra info regarding png compression. – fvu Sep 09 '11 at 14:34
Thanks for the link! Am trying `quality 02` etc but not getting anywhere. Maybe I need OptiPNG. – Richard Sep 09 '11 at 14:49
@richard fixing the first digit to 9 (for max. compression) won't hurt I think. But you may be right. – fvu Sep 09 '11 at 15:07
I ended up doing batch process in IrfanView on a Windows machine :-/ – Richard Sep 14 '11 at 12:38

Imagemagick convert massively increasing filesize?

1 Answers1